WASHINGTON (Reuters) – U.S. President Donald Trump grudgingly waived U.S. sanctions on Iran on Friday but aides said it would be the last time he would do so unless the 2015 Iran nuclear deal can be strengthened to inhibit Tehran’s nuclear and ballistic missile programs.

A senior administration official said Trump wants the 2015 Iran deal strengthened with a follow-on agreement in 120 days or the United States will unilaterally withdraw from the international pact.

Trump had privately chafed at having to once again waive sanctions on a country he sees as a rising threat in the Middle East. The official said his action on Friday “will be the last such waiver he will issue.”

Trump had lengthy discussions on Thursday with Secretary of State Rex Tillerson, national security adviser H.R. McMaster and others about the deal, which was reached during the presidency of Democrat Barack Obama.

Trump will work with European partners on a follow-on agreement that enshrines certain triggers that the Iranian regime cannot exceed related to ballistic missiles, said a senior administration officials who briefed reporters on the decision.

One official said Trump would be open to remaining in a modified deal if it was made permanent.

Trump also wants the U.S. Congress to modify a law that reviews U.S. participation in the nuclear deal to include “trigger points” that if violated would lead to the United States reimposing its sanctions, the official said.

This would not entail negotiations with Iran, the official said, but rather would be the result of talks between the United States and its European allies. Work already has begun on this front, the official said.

Trump has argued behind the scenes that the nuclear deal makes the United States look weak, a senior U.S. official said. The argument for staying in, the official said, was to allow time to toughen the terms of the agreements.

A decision to withhold a waiver would have effectively ended the deal that limits Iranâs nuclear program. The 2015 agreement between the United States and Iran also was signed by China, France, Russia, Britain, Germany and the European Union, and these countries would have been unlikely to join the United States in reimposing sanctions.

U.S. President Donald Trump addresses a joint news conference with Norwegian Prime Minister Erna Solberg in the East Room of the White House in Washington, U.S., January 10, 2018. REUTERS/Jonathan Ernst

Two senior Trump administration officials told Reuters on Wednesday that the president, a Republican, had privately expressed reluctance to heed the advice of top advisers recommending he not reimpose the suspended sanctions.

Trump has argued that Obama, a Democrat, negotiated a bad deal for the United States in agreeing to the nuclear accord.

Hailed by Obama as key to stopping Iran from building a nuclear bomb, the deal lifted economic sanctions in exchange for Tehran limiting its nuclear program.

PRESSURE FROM EUROPE

Trump had come under heavy pressure from European allies to issue the sanctions waiver.

Iran says its nuclear program is only for peaceful purposes. It has said it will stick to the accord as long as the other signatories respect it but will âshredâ the deal if Washington pulls out.

The U.S. Congress requires the president to decide periodically whether to certify Iranâs compliance with the deal and issue a waiver to allow U.S sanctions to remain suspended.

Trump in October chose not to certify compliance and warned he might ultimately terminate the accord. He accused Iran of ânot living up to the spiritâ of the agreement even though the International Atomic Energy Agency says Tehran is complying.

Hard-liners on Iran in the U.S. Congress have called for the reimposition of the suspended sanctions and an end to the nuclear deal, while some liberal Democrats want to pass legislation that would make it harder for Trump to pull Washington out without congressional consent.

Trump and his top advisers have been negotiating with U.S. lawmakers on Capitol Hill to try to change sanctions legislation so that he does not face a deadline on whether to recertify Iranian compliance with the nuclear deal every 90 days.

Senate Foreign Relations Committee Chairman Bob Corker has been working on amending a U.S. law to include âtrigger pointsâ that if crossed by Iran would automatically bring back U.S. sanctions.

Britain, France and Germany called on Trump on Thursday to uphold the pact. French President Emmanuel Macron stressed to Trump in a telephone call on Thursday the importance of abiding by the deal.

Additional reporting by Doina Chiacu and David Alexander; Editing by Yara Bayoumy and Bill Trott